A senior State Department official said that "activity of concern" was detected in the email system around the same time as the White House incident, which was made public in late October, although there was no indication then that the department had been affected. They added that none of the department’s classified systems were compromised, however.

Trying to keep the incident under wraps, the department on Friday shut down its worldwide email, saying that maintenance would be done to the unclassified computer network during a scheduled outage of some of its Internet-linked systems, but officials later acknowledged that they had found evidence of a hacking attempt, and are beefing up security of the unclassified network in the middle of a scheduled outage.

It isn't yet known how many of the department’s e-mail accounts were affected, or whether the employees' personal information was exposed.

The State Department incident is the latest in a series of security breaches that have affected a number of government agencies, including the US Postal Service and the National Weather Service.

After the White House incident, US officials pointed fingers at Russian hackers. When asked to comment on the accusations, a spokesman for Russian President Vladimir Putin dismissed them saying they can't be taken seriously unless they are backed by actual evidence.